It is known that underground mining of coal is highly expensive, and after extraction the coal has to be transported over long distances, e.g. to be used in conventional coal power stations for the generation of electrical energy. It is also known that coal power stations, generally even those equipped with the most sophisticated filter devices for the filtration of exhaust gases (such as baghouses, cyclones, scrubbers or electrostatic precipitators) which result from the combustion of coal, produce considerable amounts of filtrated material (typically fly ash). This ash must be disposed-of or utilized as construction material, (e.g., fill) or as an admixture for construction materials (e.g. concrete aggregate). In addition, conventional coal power stations naturally produce, due to the combustion of coal, considerable amounts of bottom ash and slag, which must be disposed-of or used for another appropriate purpose.
Under the aspect of the protection of the environment as well as the environmental impact, coal power stations are highly problematic, due to the necessity of providing environmentally acceptable disposal sites for the waste ash and slag and also the filtrated fly ash collected. Due to the long distances which have to be overcome for transportation between the location of coal extraction, the locations of the use of coal in the power station and the location of the disposal site, the price of the energy generated by the coal station is increased by a considerable degree.